Inspiratory effort and respiratory mechanics in spontaneously breathing patients with acute exacerbation of idiopathic pulmonary fibrosis: a retrospective matched control study.

Background- Patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) may experience severe acute respiratory failure, even requiring ventilatory assistance. Physiological data on lung mechanics during these events are lacking. Methods- Patients with AE-IPF admitted to Respiratory Intensive Care Unit to receive noninvasive ventilation (NIV) were retrospectively analyzed. Esophageal pressure swing (ΔP es ) and respiratory mechanics before and 2 hours after NIV start were collected as primary outcome. Correlation between positive end-expiratory pressure (PEEP) levels and changes of dynamic compliance (dynC RS ) and PaO 2 /FiO 2 ratio was assessed. Further, an exploratory comparison with a historic cohort of ARDS patients matched 1:1 by age, sequential organ failure assessment score, body mass index and PaO 2 /FiO 2 level was performed. Results- At baseline, AE-IPF presented high respiratory drive activation with ΔPes = 27 (21–34) cmH2O, respiratory rate (RR) = 34 (30–39) bpm and minute ventilation (VE) = 21 (20–26) L/min. Two hours after NIV application, ΔPes, RR and VE showed a significant reduction (16 [14–24] cmH2O, p<0.0001, 27 [25–30] bpm, p=0.001, and 18 [17–20] L/min, p=0.003, respectively) while no significant change was found for dynamic transpulmonary pressure (27 [21–34] VS 27 [25–36] cmH2O, p=0.2) expiratory tidal volume (Vte) (9.1 [8.7–10.1] VS 9.3 [8.7 – 9.9] mL/kg of predicted boy weight, p=0.2), dynCRS (28 [19–31] VS 26 [18–28] mL/cmH2O, p=0.1) and dynamic mechanical power (71 [49–94] VS 60 [51–74] J/min, p=0.1). PEEP levels negatively correlated with PaO 2 /FiO 2 ratio and dynC RS (r=–0.67, p=0.03 and r=–0.27, p=0.4, respectively). When compared to AE-IPF, ARDS patients presented lower baseline ΔP es , RR, VE and dynamic mechanical power. At difference with AE-IPF, Vte and dynC RS increased significantly following NIV (p=0.01 and p=0.004 respectively) with PEEP levels directly associated with PaO 2 /FiO 2 ratio and dynC RS (r=0.24, p=0.5 and r=0.65, p=0.04, respectively). Conclusions- In this study, patients with AE-IPF showed a high inspiratory effort, whose intensity was reduced by NIV application without significant improvement in respiratory mechanics. In an exploratory analysis, AE-IPF patients showed a different mechanical behavior under spontaneous unassisted and assisted breathing compared with ARDS of similar severity.